The present invention relates to a liquid crystal display (xe2x80x9cLCDxe2x80x9d) device in which TCPs are mounted on a liquid crystal panel.
Conventionally, the mounting architecture between a liquid crystal panel and driver ICs in an LCD device adopts a TCP (Tape Carrier Package) method chiefly. An LCD device mounted using the TCP method is shown in FIGS. 7A and 7B. FIG. 7A is a schematic perspective view of the LCD device, and FIG. 7B is a schematic enlarged view of a source TCP (or a gate TCP) used in FIG. 7A.
Referring to FIGS. 7A and 7B, the LCD device 500 has, on peripheries of a liquid crystal panel 501, gate TCPs 502 and source TCPs 503 for feeding signals to gate signal lines and source signal lines, respectively, of the liquid crystal panel 501, and external circuit boards 504 for feeding external signals to those TCPs 502, 503.
As shown in FIG. 7B, the gate TCP 502 and the source TCP 503 each have, on a flexible substrate 506, a liquid crystal driver IC 505, signal input lines 507 for feeding external signals (image data signal, IC driving power supply voltage, counter-electrode driving power supply voltage, etc.) to the liquid crystal driver IC 505, and signal-output lines 508 for feeding signals output from the liquid crystal driver IC 505 to the liquid crystal panel 501.
The signal input lines 507 of each TCP 502, 503 are electrically connected to terminals on the circuit boards 504 located outside the liquid crystal panel 501, by which external signals are led from the terminals on the circuit boards 504 to the liquid crystal drivers IC 505.
In this LCD device 500 adopting the TCP method, since signals are supplied directly and individually from the external circuit board 504 to the TCPs 502, 503, a very large number of wirings are necessitated on the external circuit board 504. This has caused hitherto such disadvantages as complicated fabrication process, cost increase and lowered reliability.
Thus, for the TCP method, there has been introduced in recent years a so-called xe2x80x9csignal propagation methodxe2x80x9d in which a signal, after once input to one TCP, is propagated to adjacent TCPs one after another. This method is disclosed in, for example, Japanese Patent Laid-Open Publication HEI 4-313731, Japanese Utility Model Laid-Open Publication HEI 3-114820, and Japanese Patent Laid-Open Publication HEI 10-214858.
A detailed structure of a gate TCP or source TCP mounted on an LCD device adopting the signal propagation method is as follows. That is, on a flexible substrate are mounted a liquid crystal driver IC, signal input lines for inputting external signals to the liquid crystal driver IC, signal-output lines for feeding image signals from the liquid crystal driver IC to the liquid crystal panel, and lines (hereinafter, referred to as xe2x80x9crelay linesxe2x80x9d) for outputting a liquid crystal driving signal to the adjacent TCP.
Meanwhile, connecting lines for connecting adjacent TCPs to each other are provided on peripheral portions of a substrate of the liquid crystal panel, between regions where the TCPs are mounted.
Signal propagation paths between adjacent two TCPs (designated as a first TCP and a second TCP) are explained below.
First, when external signals are fed from the circuit board to a first liquid crystal driver IC via the signal input lines, image signals responsive to these signals are sent to the liquid crystal panel via the liquid crystal driver IC and the signal-output lines.
Meanwhile, part of the external signals inputted to the first TCP are led to the relay lines of the first TCP and then fed to the input signal lines of the second TCP via the connecting lines provided on the liquid crystal panel between these first and second TCPs.
Accordingly, once signals are input from the circuit board to one TCP, part of the signals are supplied to pixels of the liquid crystal panel via the liquid crystal driver IC of the TCP, while the rest of the signals are propagated to adjacent TCPs sequentially via the relay lines of the TCPs and the connecting lines of the liquid crystal panel.
As shown above, the signal propagation method allows the number of wirings, which are necessary for input from the external circuit board to the TCPs, to be considerably reduced, as compared with the TCP method. Thus, this method is effective for cost reduction of circuit boards.
Aforementioned Japanese Patent Laid-Open Publication HEI 4-313731 and Japanese Utility Model Laid-Open Publication HEI 3-114820 suggest that the need of external circuit boards can be eliminated by providing bus lines, which run longitudinally over the entire peripheral part of the liquid crystal panel while bending again and again, in order to propagate signals to the individual TCPs sequentially.
In this manner, the two publications disclose a method for dispensing with the external circuit boards. However, the technique disclosed in these two publications incurs high wiring resistance because of the bus lines being very long. Also, since the wirings of the liquid crystal panel generally need to be provided on a glass substrate, it is inevitable to use wirings much higher in resistance value than those of the external circuit boards or TCPs, resulting in further increase of the wiring resistance. This in return causes problems such as propagation delay of signals. Besides, the publications make no mention of signals that are to be introduced. So, there may occur problems in practical use. In particular, a large voltage drop due to wiring resistance in the power supply voltage for driving the liquid crystal driver IC of the TCP, the power supply voltage for driving counter-electrodes, and the like, may cause operational problems. For prevention of this, signals need to be propagated under low resistance. Thus, for those signals, actually, circuit boards 504 would inevitably be provided as shown in FIG. 8A, where signals are inputted from the circuit boards 504 to the TCPs separately and individually.
Japanese Patent Laid-Open Publication HEI 10-214858 discloses that a power supply voltage line for driving the liquid crystal driver IC extends from one end to the other end of the TCP. In such a case, connecting the power supply voltage lines of the adjacent TCPs to each other makes it possible to dispense with the external circuit boards shown in FIG. 8A. Also, since the connection of the adjacent TCPs to each other is only required, it is unnecessary to form such a long bus line as runs over the entire peripheral part of the liquid crystal panel, as would be involved in the technique disclosed in the foregoing two publications. However, because the third publication does not at all disclose a wiring structure for propagating on the TCP a signal which does not need to be input to the liquid crystal driver IC but which is to be output to the pixel section of the liquid crystal panel, such as for counter-electrode voltage lines, use of such signals would incur inconvenience in the implementation of the technique of this publication. Further, the TCP disclosed in the third publication has a structure that connecting terminals are not arranged along just one side edge of the TCP but a plurality of side edges thereof. On this account, there is a problem that an application process of an anisotropic conductive tape involved in the bonding of the TCPs to the liquid crystal panel is complicated.
The present invention having been accomplished to solve these and other problems, an object of the invention is to provide an LCD device which dispenses with the external circuit boards to thereby realize reduction in module size and weight at low costs and without incurring any disadvantages or inconveniences.
According to an aspect of the invention, there is provided a liquid display device (LCD) comprising:
a liquid crystal panel having a plurality of electrode terminals provided in a peripheral part thereof and a pixel section provided in a central part thereof; and
a plurality of wiring boards each provided with a liquid crystal driver IC and wirings, wherein
the wirings comprise first wirings for supplying signals to the pixel section and second wirings contributing to signal transfer and reception between mutually adjacent wiring boards;
the plurality of wiring boards each have one generally belt-shaped terminal connection area extending along one longitudinal edge of the wiring board; and
the first wirings are electrically connected to their respective corresponding electrode terminals of the liquid crystal panel in a lengthwise central part of the terminal connection area, while the second wirings are electrically connected to their respective corresponding electrode terminals of the liquid crystal panel in either lengthwise end portion of the terminal connection area.
The LCD device of the present invention is of the signal propagation type. The plurality of wiring boards mounted on the LCD device each have a plurality of connecting terminals within a generally belt-shaped area (the terminal connection area) located in a peripheral part thereof, and the connecting terminals are electrically connected to the electrode terminals on the liquid crystal panel within the area. Of the connecting terminals on each wiring board, terminals (the first wirings) for feeding signals to the pixel section are provided in a longitudinally central portion of the generally belt-like area and terminals (the second wirings) which contribute to signal transfer and reception with the adjacent wiring boards are provided closer to either end of the generally belt-like area than the first wirings. Like this, because the terminal connection area is generally belt-shaped, the connection between the wiring boards and the liquid crystal panel can be achieved collectively. Also, because the terminals contributing to signal transfer and reception in one wiring board are provided close to the terminals contributing to signal transfer and reception in the adjacent wiring boards, the signal transfer and reception between wiring boards can be achieved under very low resistance even in the signal propagation LCD device. Thus, according to the present invention, it becomes possible to do away with the external circuit board, which in turn allows reduction in the component member cost, reduction in the number of process steps by elimination of the connecting process for the external circuit board, enhancement in the rate of conforming articles by the reduction of process steps, reduction in the device thickness and the number of assembly steps by simplification of the module form, and so on.
In at least part of the wiring boards, the first wirings may include a first signal line for feeding a first signal (e.g., counter voltage) to the pixel section, and the second wirings may include a second signal line for feeding the first signal to the adjacent wiring board, the first signal line and the second signal line being electrically connected to each other on the wiring board. With this arrangement, the counter voltage, for example, can be fed to the liquid crystal panel without intersecting any other wirings on the liquid crystal panel. Besides, propagation paths of the counter voltage can be lowered in resistance to a possible minimum.
The first signal line and the second signal line may be electrically connected to each other by means of a jumper bridging other wirings. With this arrangement, the two signal lines can be connected to each other with low resistance and by a simple process. Further, because the two signal lines can be connected without enlarging the area of the wiring board, the picture-frame width of the LCD device can be kept to a minimum.
Alternatively, the first signal line and the second signal line may be electrically connected to each other by means of a routing line at a site outside the terminal connection area. With this arrangement, these two lines can be connected to each other without involving any increase in fabrication process of the wiring board and with low resistance. It is noted that although the first and second signal lines and the routing line have been referred to as separate designations, the first or second signal line may serve also as the routing line.
Additionally to the arrangement described immediately before, two first signal lines may be included within each of the wiring boards, and the two first signal lines may be electrically connected to each other by means of a routing line at a site outside the terminal connection area. With this arrangement, because the first signal fed from the second signal line can be output from two places to the pixel section, the first signal lines themselves can be lowered in resistance, thereby making it possible to prevent delays of the first signal, voltage drops and the like. Further, using this routing line makes it possible for one wiring board to simply transfer the first signal fed from its preceding-stage wiring board to its succeeding wiring board. It is noted that although the first signal lines and the routing line have been referred to as separate designations, either first signal line may serve also as the routing line.
Any one of the second wirings of each wiring board may have an end portion that extends up to a side edge of the wiring board, the side edge facing a side edge of the adjacent wiring board. With this arrangement, the distance between these second wirings on the adjacent wiring boards is made the shortest and eventually the signal transfer and reception between those second wirings is achieved under low resistance. Further, for example, if the second wiring is bent at its opposite end portions as will be described later, end portions of a plurality of second wirings can be made to extend up to the side edge of the wiring board facing its adjacent wiring board. Therefore, signal transfer and reception can be achieved under low resistance with a plurality of wirings.
In one embodiment, the second wirings of each wiring board are electrically connected to the second wirings of the adjacent wiring board by means of connecting lines provided on the liquid crystal panel. With this arrangement, the connecting lines used for signal transfer and reception between wiring boards can be shortened as much as possible and moreover the signal transfer and reception can be achieved under as low resistance as possible.
The connecting lines include high-resistance wirings and low-resistance wirings, and the second signal line of each wiring board may be electrically connected to the second signal line of the adjacent wiring board by means of a low-resistance wiring. With this arrangement, delays of the first signal, voltage drops and the like can be prevented. It is noted here that the term xe2x80x9clow-resistance wiringxe2x80x9d means a wiring that has a resistance lower than that of the high-resistance wiring. The connecting lines could be classified generally into several types (two types in an embodiment shown in FIG. 2B) in terms of line length, line width and the like, as described later. In such a case, the low-resistance wirings are those belonging to a kind whose resistance is the lowest among the several kinds.
Also, in at least part of the wiring boards, a third wiring having both a function of outputting a signal to the pixel section and a function of contributing to signal transfer and reception with the adjacent wiring board may be located between the first wirings and the second wirings. With this arrangement, the number of connecting terminals between the wiring boards and the liquid crystal panel can be reduced.
Also, those wiring boards may each have two third wirings, and the two third wirings may be electrically connected to each other by means of a routing line at a site outside the terminal connection area. With this arrangement, because the signal fed from the third wiring can be outputted from two places to the pixel section, the third wirings themselves can be lowered in resistance, thereby making it possible to prevent signal delays, voltage drops and the like. Further, use of the routing line makes it possible for one wiring board to simply transfer the signal fed from its preceding-stage wiring board to its succeeding wiring board. It is noted that although the third wirings and the routing line have been referred to as separate designations, the third wiring may be used as the routing line also.
Also, the third wirings of one wiring board may be electrically connected to the third wirings of the adjacent wiring boards by means of connecting lines provided on the liquid crystal panel. With this arrangement, the connecting lines used for signal transfer and reception between wiring boards can be shortened as much as possible and moreover the signal transfer and reception can be achieved under the lowest possible resistance.
Also, in at least part of the wiring boards, a grounding terminal may be exposed at a surface of each wiring board and kept in direct contact with an external grounding terminal. With this arrangement, the connecting resistance can be further lowered.
Other objects, features and advantages of the present invention will be obvious from the following description.